Liver damage is one of the well-known consequences of excessive alcohol consumption, but at least it’s a sign of having fun, right? Not always, it turns out. Some gut bacteria produce alcohol, and may be damaging your liver without even giving you the temporary pleasures of drinking, which seems a bit unfair.
About a quarter of the world’s adults suffer from non-alcoholic fatty liver disease (NAFLD) where fat builds up in the liver, impeding its function, without excessive drinking. Its cause is unknown, but a paper in Cell Metabolism suggests the name is often a bit misleading.
Jing Yuan of China’s Capital Institute of Pediatrics and colleagues studied a patient who had severe NAFLD and also got drunk every time he ate sugar-rich foods, a condition known as auto-brewery syndrome (ABS). ABS is normally associated with yeast infections, but this patient apparently didn't have one – both coming up negative on tests and not responding to anti-yeast medications.
Yuan delved deeper and found the alcohol was coming from gut bacteria. "We were surprised that bacteria can produce so much alcohol," Yuan said in a statement. "When the body is overloaded and can't break down the alcohol produced by these bacteria, you can develop fatty liver disease even if you don't drink." The authors studied the feces of people in this situation to identify the specific bacteria responsible and put the blame on specific Klebsiella pneumonia strains.
Although almost everyone has K. pneumonia in their digestive system, most produce only tiny amounts of alcohol. The strains Yuan found in people with NAFLD produce four to six times as much alcohol as the more common varieties, equivalent to turning a single glass of wine into a nightly bottle.
Yuan found 60 percent of a sample of Chinese people who suffer from NAFLD have gut bacteria that produce considerable amounts of alcohol, although seldom enough to produce obvious signs of intoxication. Put another way, one in seven people’s guts make enough alcohol to harm their health without getting slightly buzzed, let alone reveling in the taste of a fine wine or whisky.
To confirm all this undrunk alcohol really is responsible for NAFLD, Yuan fed mice high-fermentation K. pneumonia strains, and within a month their livers were showing fat build-ups. After an additional month the livers were scarred, indicating long-term damage. Removing the K. pneumonia stopped the effects.
"NAFLD is a heterogenous disease and may have many causes," Yuan said. "Our study shows K. pneumonia is very likely to be one of them. These bacteria damage your liver just like alcohol, except you don't have a choice.” Work continues both on identifying why the fermenting strains infect some people and not others, and on finding treatments, aside from the obvious route of reducing sugar intake.
Unless you have exceptional quantities, K. pneumonia won't cause these effects on the brain, but it can do bad things to the liver.